12CO J=2−1 and 12CO J=3−2 observations toward the high-mass protostellar candidate IRAS 20188+3928

Abstract

We have carried out observations of 12CO J=2−1 and 12CO J=3−2 toward the high-mass protostellar candidate IRAS 20188+3928. Compared with previous observations, the 12CO J=2−1 and 12CO J=3−2 lines both have asymmetric profiles with an absorption dip. The velocity of the absorption dip is ∼ 1.0 km s−1. The spectral shape may be caused by rotation. The velocity-integrated intensity map and position-velocity diagram of the 12CO J=2−1 line present an obvious bipolar component, further verifying that this region has an outflow motion. This region is also associated with an HII region, an IRAS source, and an H2O maser. The H2O maser has the velocity of 1.1 km s−1. Compared with the components of the outflow, we find that the H2O maser is not associated with the outflow. Using the large velocity gradient model, we concluded that possible averaged gas densities of the blueshifted lobe and redshifted lobe are 1.0×105 cm−3 and 2.0×104 cm−3, while kinetic temperatures are 26.9 K and 52.9 K, respectively. Additionally, the outflow has a higher integrated intensity ratio (ICO J=3−2/ICO J=2−1).